The _final_ causes of many of these facts are easy to comprehend: the reason why a root grows down into the earth, is for the purpose of obtaining that sustenance which is necessary for the growth of the plant of which it is a part; and stems grow upwards, and towards the light, because the influence of this element is necessary for the elaboration of the sap; as a result of which process, stems grow in thickness, roots in length, flowers are developed, and the proper juices of vegetables become formed. We are likewise not without the means of explaining the _proximate_ cause of one of these phenomena, for we have shown in our articles on Vegetable Sap that it is by the ascending sap that stems grow in length, and that, when light is excluded, no other sap can be formed; this causes the ascending sap to accumulate under such circumstances, and, consequently, in the dark, stems may be expected to acquire an enormous and very disproportionate length: thus we are enabled to understand why the potato, in the instance mentioned, should grow to so great a height. But admitting this explanation, how much seems incomprehensible in these common and too frequently neglected phenomena! We shall endeavour, in this and the following articles, to explain the manner in which these curious things occur. One might imagine that the reason why roots grow into the earth, and stems grow out of it, is on account of the former being attracted, and the latter repelled, by the materials of which that earth is composed; or, on the other hand, by the stems being attracted, and roots repelled, by atmospheric air. But such cannot be the case; for if seeds be made to germinate in the lower stratum of earth placed in a box furnished with holes in the bottom, the roots will descend into the air through those holes, while the stems will ascend into the earth. In a similar manner, it might and has been thought that roots are attracted, and stems repelled, by the moisture of the earth; but a seed made to germinate between two moist sponges will protrude its root downwards, and its stem upwards, without reference to the liquid in its vicinity. This explanation is therefore equally inadmissible. There are some who explain these, as well as all other things occurring in living beings, by the mysterious principle of life; but we only admit the existence of this principle, because there are some phenomena incapable of being accounted for by the ordinary laws that rule the universe, and that are common to all matter; and it is therefore unphilosophical to ascribe any effects to its operation, until they are found to be inexplicable by those ordinary laws. But we shall find that the facts in question do not in a great measure belong to these exceptions.